The answer to all of the questions can be found in the theme line of Kenny Roger's song The Gambler: "You've got to know when to hold'em, know when to fold'em."
Probably the biggest difference between winning and losing players is that the losers don't know when to get away from a hand. They continue to "chase" (call the hand all the way down) and hope to get lucky. There's an old adage in poker that says: "If you can't beat a calling station, you can't beat anybody." This is true. Calling stations are losing poker players.
Certainly, to become a winner, selecting a good starting hand is extremely important (probably the most important thing for beginners). But regardless of what you start with, knowing how and when to jettison a hand is the key to successful poker.
We all see weak players who play a lot of hands. Bad players are considered "bad" because they play too many hands. Well, I've got a secret to share with you. Many of the best players also play a lot of hands! You might be wondering, "How can that be? How can some players who play a lot of hands be “bad” players and others who play a lot of hands be "great" players?”
There are two major reasons. First, the top players are betting and raising while the weak players are checking and calling. Second, and most important, the top players know when to get away from a hand. It doesn’t matter how strong the hand is. If a top player knows that he is beat, the hand is going straight to the muck. Also, the strong players know when their mediocre hand is the best hand. As such, they will bet it all the way down. As the song says, they know when to hold’em and know when to fold'em.
To illustrate, here's an example: Assume that a player held the 7 9 and the flop came Q-10-8. A bad player would look at this board and think that a Jack would give them a straight. While this is true, what the bad player doesn’t realize is that even if he were to make the straight it is what we call the ignorant (wrong) end of the straight. Good players would virtually never call and continue to play after the flop. They would simply throw the hand away.
In Omaha (high and high-low split), one mistake that weak players make is drawing to straights and flushes when there is a pair on the board. Good players rarely do this. In Omaha eight-or-better, how many times do you see weak players calling raises when drawing to a low that is not even the "nuts" (to say nothing of their hoping to win just half the pot)? It happens all the time. This kind of play is throwing money away in the long run.
You will become a much better poker player by not "chasing." Learn to throw your hand away and don't worry about being bluffed out. Players who never get bluffed out of pots, are losing players. Instead, worry about the money you are wasting by calling hands to the river. Saving bets will put a lot of money in your pocket at the end of the year. As Mike Caro likes to say, "Money saved is money earned."